So-called “impregnated” drag bits are used conventionally for drilling hard and/or abrasive rock formations, such as sandstone. The impregnated drill bits conventionally employ a cutting face composed of superabrasive particles, such as diamond grit, dispersed within a matrix of wear resistant material. As such a bit drills, the matrix and embedded diamond particles wear, cutting particles are lost as the matrix material wears, and new cutting particles are exposed. These diamond particles may either be natural or synthetic, and may be cast integral with the body of the bit, as in low-pressure infiltration, or may be preformed separately, as in hot isostatic pressure (HIP) infiltration, and attached to the bit by brazing or furnaced to the bit body during manufacturing thereof by an infiltration process, if the bit body is formed of, for example, tungsten carbide particles infiltrated with a metal alloy binder.
During the drilling of a well bore, the well may be drilled in multiple sections wherein at least one section is drilled, followed by the cementing of a tubular metal casing within the borehole. In some instances, several sections of the well bore may include casing of successively smaller sizes, or a liner may be set in addition to the casing. In cementing the casing (such term including a liner) within the borehole, cement is conventionally disposed within an annulus defined between the casing and the borehole wall by flowing the cement downwardly through the casing to the bottom thereof and then displacing the cement through a so-called “float shoe” such that it flows back upwardly through the annulus. Such a process conventionally results in a mass or section of hardened cement proximate the float shoe and formed at the lower extremity of the casing. Thus, in order to drill the well bore to further depths, it becomes necessary to first drill through the float shoe and mass of cement.
In other instances, during drilling a well bore, the well bore must be “side tracked” by drilling through the casing, through cement located outside the casing, and into one or more formations laterally adjacent to the casing to continue the well bore in the direction desired.
Conventionally, a drill bit used to drill out cement and a float shoe to drill ahead of the existing well bore path does not exhibit the desired design for drilling the subterranean formation which lies therebeyond. Thus, those drilling the well bore are often faced with the decision of changing out drill bits after the cement and float shoe have been penetrated or, alternatively, continuing with a drill bit which may not be optimized for drilling the subterranean formation below the casing.
Also, a drill bit used to drill out casing for continuing boreholes in a directional well does not exhibit the desired design for drilling the subterranean formation which lies therebeyond. Thus, those drilling the well bore are often faced with the decision of changing out drill bits after the casing and cement have been penetrated or, alternatively, continuing with a drill bit which may not be optimized for drilling the subterranean formation adjacent to the casing.
In very hard and abrasive formations, such as the Bunter Sandstone in Germany, conventional side track bits wear out quickly, often before cutting a complete window in the casing and in general within a few meters, during the high build angle toward a lateral wellbore path.
Thus, it would be beneficial to design a drill bit which would perform more aggressively in softer, less abrasive formations while also providing adequate rate of penetration (ROP) and enhanced durability in harder, more abrasive formations without requiring increased weight-on-bit (WOB) during the drilling process.
Additionally, it would be advantageous to provide a drill bit with “drill out” features that enable the drill bit to drill through casing, cement outside the casing, or a cement shoe and continue drilling the subsequently encountered subterranean formation in an efficient manner for an extended interval.